Mathematics – Logic
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...211.9614h&link_type=abstract
American Astronomical Society, AAS Meeting #211, #96.14; Bulletin of the American Astronomical Society, Vol. 39, p.902
Mathematics
Logic
Scientific paper
By virtue of their size, galaxy clusters can be used to place important constraints on cosmological parameters. In particular, charting the evolution of the cluster mass function provides us with vital information on the progression of large-scale structure formation over time. The masses of clusters, however, are often inferred from observables such as gas temperature or X-ray luminosity, which can be influenced by non-gravitational processes that affect cluster baryons, such as energy injection (heating) and radiative cooling. In addition, many high-redshift cluster surveys select samples based on baryon observables such as gas density. Recent correlations between temperature, luminosity, and total cluster mass indicate significant discrepancies between observations and the theoretical expectations of self-similarity. Therefore understanding changes in cluster properties with redshift is of crucial importance to surveys that intend to use the evolution of the cluster population as a proxy for cosmic evolution, and ultimately for the determination of cosmological parameters. Here we present the final results of our X-ray investigation of 13 high-redshift (0.6 < z < 1.1) optically-selected clusters from the Red-sequence Cluster Survey (RCS). Using a comparison sample consisting of moderate redshift (0.1 < z < 0.6) X-ray selected clusters, we find clear discrepancies in the normalizations of all scaling relationships involving baryon density (e.g., L-T). These results suggest that basic gravitational collapse is not the only process that regulates baryon heating in the potential wells of clusters, and that the central entropy of these high-z objects has been elevated by processes such as pre-heating, mergers, and episodic AGN outbursts. Perhaps most importantly, the ratio of gas mass to total gravitating mass is systematically lower in our high-redshift sample, presenting a challenge to cluster surveys that rely (implicitly or explicitly) on the assumption of constant gas mass fraction to detect clusters and/or determine their masses.
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